Communication terminal apparatus, distribution apparatus, error notification method, and error notification program

ABSTRACT

A communication terminal apparatus ( 130 ) includes a receiving unit ( 132 ) that receives distribution data distributed through a unidirectional communication network ( 210 ), an OS/application unit ( 131 ) that accepts transmission data to a tunneling apparatus ( 120 ), and a communication processing unit ( 133 ) that transmits the transmission data to a bidirectional communication network ( 220 ). When the communication processing unit ( 133 ) detects an error message of an encapsulated packet from the network ( 220 ) using a detecting unit ( 134 ), a setting unit ( 135 ) sets new transmission data that includes the error message. An error processing unit ( 136 ) subjects the transmission data to a process of resolving the error and thereafter, the transmission data is again transmitted to the network ( 220 ) to use the transmission data as distribution data from the tunneling apparatus ( 120 ).

TECHNICAL FIELD

The present invention relates to a communication terminal apparatus thatreceives using a unidirectional communication network and that transmitsusing a bidirectional communication network, a distribution apparatusthat distributes distribution data using a unidirectional communicationnetwork and that receives transmission data from each terminal being adistribution destination of the distribution data using a bidirectionalcommunication network, and an error notification method and an errornotification program of the above apparatuses.

BACKGROUND ART

Conventionally, to transmit and receive data using a network such as theInternet, connection to a communication counterpart terminal apparatusis established through a LAN (Local Area Network) or a WAN (Wide AreaNetwork) that is configured according to any one of various standardssuch as Ethernet (a registered trade mark), an FDDI (Fiber-DistributedData Interface), and an ATM (Asynchronous Transfer Mode).

A given relay apparatus such as a router is equipped between networks.The relay apparatus has a function of monitoring whether transmissiondata transmitted to a network is transmittable. Therefore, when therelay apparatus finds an error in the transmission data, the relayapparatus transmits an error message corresponding to the content of theerror to a communication terminal apparatus that is the transmissionsource of the transmission data.

An error message may be, for example, a packet too big message, adestination unreachable message, a time exceeded message, and aparameter problem message. The details of processing for using a networkbased, in particular, on the IPv6 (Internet Protocol Version 6) will bedescribed taking an example where a packet-capacity exceeded message istransmitted from a relay apparatus.

(MTU of Network)

As described, to transmit and receive data between given terminalapparatuses using the Internet, multiple networks must be passed throughusing relay apparatuses. The networks each have set therein apermissible data size that is transmittable for one packet oftransmission. This permissible amount is generally referred to as “MTU(Maximum Transmission Unit)”. When multiple networks are passed throughto transmit and receive data between communication terminal apparatuses,a terminal apparatus for transmission must adjust the capacity oftransmission data such that the transmission data may be transferredthrough the network having the smallest MTU.

FIG. 10 is a diagram for explaining a monitoring process of transmissiondata by a relay apparatus. The relay apparatus not only relays betweennetworks but also monitors the capacity of transmission data such that aterminal apparatus for transmission may transmit transmission data of acapacity corresponding to the MTU of a network.

As depicted in FIG. 10, two networks, a network A and a network B, areconfigured between two communication terminal apparatuses 1000 and 1010.Relay apparatuses R1 and R2, and R3 and R4 are respectively disposed inthe networks A and B. Explanation will be given assuming that thecommunication terminal apparatus 1010 is a terminal for transmission,the communication terminal apparatus 1000 is a terminal for reception,and the MTU of the networks A and B is 1,500 [bytes].

To transmit transmission data from the communication terminal apparatus1010, a case is tentatively assumed first where the transmission data isoutput from an application unit 1011 to communication processinginterfaces (I/Fs) 1012A and 1012B (S10). A process of actuallyoutputting packets using application software simultaneously to twointerfaces is not common. However, to describe the relation between thetransmission data and the MTU, a case where the transmission data isoutput to the communication processing interfaces (I/Fs) 1012A and 1012Bis temporarily assumed and will be described for convenience.

In this example, transmission data of a capacity of 1,500 [bytes] orless, representing packet size, is output to the communicationprocessing interface (I/F) 1012A and transmission data of a packet sizeof 1,500 [bytes] or larger is output to the communication processinginterface (I/F) 1012B.

The transmission data transmitted from the communication processinginterface (I/F) 1012A to the network A has a capacity equal to or lessthan the MTU and therefore, the transmission data is received by thecommunication processing interface (I/F) 1001A of the communicationterminal apparatus 1000 for reception through the relay apparatuses R2and R1 (S11).

On the other hand, the transmission data transmitted from thecommunication processing interface (I/F) 1012B to the network B has acapacity exceeding the MTU and the relay apparatus R3 detects that thecapacity is larger than the MTU (S12). Hence, the transmission data isnot transmitted to the communication processing interface (I/F) 1001B ofthe communication terminal apparatus 1000 and instead, an error message“Packet Too Big” indicating that the transmission data exceeds the MTUis transmitted to the communication terminal apparatus 1010 (S13).

When the communication processing interface (I/F) 1012B of thecommunication terminal apparatus 1010 receives the error message “PacketToo Big” from the network B, the interface (I/F) 1012B reduces thepacket size of the transmission data. This series of processing is knownas “Path MTU Discovery (RFC 1981)” (see, for example, Non-PatentLiterature 1).

Recently, transmission and reception of data using a network that usesUDLR (Uni-Directional Link Routing) has also been realized. FIG. 11 is adiagram for explaining a monitoring process of a relay apparatus in anetwork using the UDLR.

As depicted in FIG. 11, the network using the UDLR includes adistribution apparatus 1100 that distributes data (distribution data)using a unidirectional communication network, and a communicationterminal apparatus 1110 that receives the transmission data. Thedistribution apparatus 1100 and the communication terminal apparatus1110 are connected to a unidirectional communication network C dedicatedfor distribution, and a bidirectional communication network D (a normalnetwork) used for transmitting data from the communication terminalapparatus 1110 to the distribution apparatus 1100.

When the distribution data is distributed from the distributionapparatus 1100 to the communication terminal apparatus 1110, thedistribution data is output from a distributing interface (I/F) 1101 tothe unidirectional communication network C (S00). From the distributionapparatus 1100, the distribution data may be distributed to a specificcommunication terminal apparatus or may be distributed to multiplecommunication terminal apparatuses as a broadcast wave.

The communication terminal apparatus 1110 receives the distribution datausing a receiving interface (I/F) 1112. In a network using the UDLR, totransmit a response to the distribution apparatus 1100, transmissiondata is output from an OS/application unit 1111 to the receivinginterface (I/F) 1112 that is connected to the unidirectionalcommunication network C (S20). To transmit as a response to thedistribution apparatus 1100, the transmission data that is transmittedas a response to the unidirectional communication network C, thereceiving interface (I/F) 1112 realizes a virtual bidirectionalcommunication network by transmitting the transmission data to thebidirectional communication network D. Therefore, the receivinginterface (I/F) 1112 applies a given process to the transmission dataand outputs the processed transmission data to a communicationprocessing interface (I/F) 1113 (S21).

The communication processing interface (I/F) 1113 transmits thetransmission data to the bidirectional communication network D. Here,when the transmission data has a capacity equal to or less than the MTU,the transmission data is transmitted to the distribution apparatus 1100through the relay apparatuses R3 and R4.

Nonpatent Literature 1: Izumi, Miki, “Serial Article: Invitation to IPv6Networks (No. 3) ‘Header Format of IPv6 ’”, [online], Oct. 5, 2001,Research Institute for Internet Strategies, Inc., [Retrieved on Jul. 7,2006], on the Internet <URL:http://www.atmarkit.co.jp/fnetwork/rensai/ipv6-03/ipv6-01.html>

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, the above monitoring process using the relay apparatuses doesnot function normally when bidirectional communication is executed usinga network for unidirectional communication.

More specifically, when transmission data having a capacity exceedingthe MTU is transmitted (S22) in FIG. 11, the relay apparatus R3 detectsthat the transmission data exceeds the MTU similarly to the exampledepicted in FIG. 10. An error message “Packet Too Big” is transmittedfrom the relay apparatus R3 to the communication terminal apparatus 1110(S23). Therefore, the transmission data is not transmitted to areceiving interface (I/F) 1102 of the distribution apparatus 1100.

The error message “Packet Too Big” is transmitted to the communicationprocessing interface (I/F) 1113 of the communication terminal apparatus1110. In this manner, the communication processing interface (I/F) 1113receives the message “Packet Too Big”. However, in the UDLR network, theinterface that actually outputs the transmission data from the apparatusis the receiving interface (I/F) 1112. Therefore, the message “PacketToo Big” does not reach the receiving interface (I/F) 1112.

Accordingly, the OS/application unit 1111 recognizes the MTU of thebidirectional communication network D and reduces the packet size of thetransmission data that is directly transmitted to the bidirectionalcommunication network D. However, when the transmission data is to betransmitted from the communication terminal apparatus 1110 to theunidirectional communication network C, the OS/application unit 1111recognizes this transmission data as transmission data to be transmittedfrom the receiving interface (I/F) 1112 to the unidirectionalcommunication network C and accordingly executes processing. Thus, theOS/application unit 1111 does not reflect at all the message “Packet TooBig” that arrives at the communication processing interface (I/F) 1113and the OS/application unit 1111 inevitably outputs, consecutively,transmission data having a packet size exceeding the MTU to thereceiving interface (I/F) 1112. In this manner, in a UDLR network, “PathMTU Discovery” do not function.

As described, in a UDLR network, error messages by a relay apparatus arenot reflected at the communication terminal apparatus 1110. Therefore,in a conventional UDLR network, to prevent the capacity of anytransmission data from exceeding the MTU, transmission is executed usingthe smallest value set as the MTU, as the capacity of the transmissiondata. Hence, only transmission data having the smallest capacity may behandled regardless of the actual MTU of a network and therefore, aproblem has arisen in that the efficiency of the communication is poor.

Even when an error message other than the packet too big message istransmitted, the error message does not reach the interface (in FIG. 11,receiving interface (I/F)) 1112 that has output the transmission datacausing the error. Therefore, a problem has arisen in that the errorwill not be resolved.

To solve the above problems associated with the conventional techniques,an object of the present invention is to provide a communicationterminal apparatus, a distribution apparatus, an error notificationmethod, and an error notification program that provide notification ofan error to an interface that is the transmission source transmittingtransmission data from which the error is detected, enabling the errorto be resolved, even using a network that is configured to receive datafrom a communication counterpart using a unidirectional communicationnetwork.

Means for Solving Problem

To solve the problems above and achieve an object, a communicationterminal apparatus according to the invention of claim 1 receives usinga unidirectional communication network and transmits using abidirectional communication network. The communication terminalapparatus includes a receiving unit that receives distribution datadistributed through the unidirectional communication network; anaccepting unit that accepts transmission data to be transmitted to adistribution source of the distribution data received by the receivingunit; and a communication processing unit that transmits thetransmission data accepted by the accepting unit to the bidirectionalcommunication network. The communication processing unit includes adetecting unit that detects an error message concerning the transmissiondata from the bidirectional communication network; a setting unit thatsets the transmission data that includes the error message detected bythe detecting unit, to be new transmission data; an error processingunit that subjects the new transmission data set by the setting unit toa process of resolving an error corresponding to the error message; anda transmitting unit that transmits the transmission data whose error hasbeen resolved by the error processing unit to the bidirectionalcommunication network to use the transmission data as the distributiondata from the distribution source.

According to the invention of claim 1, the error notification does notend with a transmission of an error message to a unit unrelated to thetransmission data setting as is conventionally executed, rather thetransmission data is processed as new transmission data that includesthe error message. The new transmission data is transmitted to thedistribution apparatus to be distributed from the distribution apparatusto the transmission source as distribution data.

Further a distribution apparatus according to the invention of claim 5includes a distributing unit that distributes distribution data using aunidirectional communication network; and a receiving unit that receivestransmission data from a terminal that is a distribution destination ofthe distribution data, using a bidirectional communication network. Thedistributing unit distributes the transmission data as the distributiondata to a terminal that is a transmission source of transmission datathat includes an error message received by the receiving unit, when thereceiving unit receives transmission data that includes an error messagefrom a terminal.

According to the invention of claim 5, when the transmission data havingincorporated therein the error message is received, the transmissiondata received is distributed as distribution data to a terminal that isthe transmission source of the transmission data. Therefore, the errormessage is directly distributed to the terminal that is the transmissionsource of the transmission data corresponding to the error message andthereby, enabling notification of the error.

An error notification method according to the invention of claim 7 isthat of a communication terminal apparatus that receives by aunidirectional communication network and transmits by a bidirectionalcommunication network. The error notification method includes areceiving step of receiving, distribution data distributed through theunidirectional communication network; an accepting step of acceptingtransmission data to be transmitted to a distribution source of thedistribution data received at the receiving step; and a firsttransmitting step of transmitting the transmission data accepted at theaccepting step to the bidirectional communication network; a settingstep of setting, when an error message is detected with respect to thetransmission data from the bidirectional communication network, thetransmission data including the detected error message to be newtransmission data; an error processing step of subjecting the newtransmission data set at the setting step to a process of resolving anerror corresponding to the error message; and a second transmitting stepof transmitting the transmission data whose error has been resolved atthe error processing step, to the bidirectional communication network touse the transmission data as the distribution data from the distributionsource.

According to the invention of claim 7, the error notification does notend with a transmission of an error message to a unit unrelated to thetransmission data setting as is conventionally executed, rather thetransmission data is processed as new transmission data that includesthe error message. After processing, the new transmission data istransmitted to the distribution apparatus to be distributed from thedistribution apparatus to the transmission source as distribution data.

An error notification method according to the invention of claim 8,includes a receiving step of receiving via a bidirectional communicationnetwork and by a transmitting unit of a distribution apparatus,transmission data from a terminal that is a distribution destination ofthe distribution data; and a distributing step of distributing via aunidirectional communication network, by a distribution unit of thedistribution apparatus and as distribution data, the transmission datato the terminal that is a transmission source of the transmission datareceived at the receiving step and inclusive of an error message.

According to the invention of claim 8, when the transmission data havingincorporated therein the error message is received, the transmissiondata received is distributed as distribution data to a terminal that isthe transmission source of the transmission data. Therefore, the errormessage is directly distributed to the terminal that is the transmissionsource of the transmission data corresponding to the error message andthereby, enabling notification of the error.

An error notification program according to claim 9 causes a computer toexecute the error notification method recited in claim 7 or 8.

EFFECT OF THE INVENTION

According to the communication terminal apparatus, the distributionapparatus, the error notification method, and the error notificationprogram of the present invention, an effect is achieved in that errornotification may be provided to an interface that is the transmissionsource transmitting transmission data from which the error is detectedand thereby, the error may be resolved even using a network that isconfigured to receive data from a communication counterpart using aunidirectional communication network.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for explaining a network configuration according tothe present embodiment;

FIG. 2-1 is a diagram for explaining an error message notificationprocess;

FIG. 2-2 is a list of addresses of configurations;

FIG. 3 is a sequence chart of a transmission route of transmission data;

FIG. 4 is a diagram of a configuration a frame of transmission data 400;

FIG. 5 is a diagram of a configuration of a frame of transmission data500;

FIG. 6 is a diagram of a configuration of a frame of transmission data600;

FIG. 7 is a diagram of a configuration of a frame of transmission data700;

FIG. 8 is a diagram of a configuration of a frame of transmission data800;

FIG. 9 is a diagram of a configuration of a frame of transmission data900;

FIG. 10 is a diagram for explaining a monitoring process of transmissiondata by a relay apparatus; and

FIG. 11 is a diagram for explaining a monitoring process of a relayapparatus in a network using the UDLR.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   110 application server    -   120 tunneling apparatus    -   121 receiving unit    -   122 distributing unit    -   123, 124 I/F (interface) unit    -   130 communication terminal apparatus    -   131 OS/application unit    -   132 receiving unit    -   133 communication processing unit    -   134 detecting unit    -   135 setting unit    -   136 error processing unit    -   137 I/F (interface) unit    -   140 a unidirectional communication network    -   140 b IPv6 relaying network    -   R1, R2, R3, R4 relay apparatus    -   Z router

BEST MODE(S) FOR CARRYING OUT THE INVENTION

A preferred embodiment of a communication terminal apparatus, adistribution apparatus, an error notification method, and an errornotification program according to the present invention will bedescribed in detail with reference to the accompanying drawings.

(Network Configuration)

A network configuration according to the present embodiment will bedescribed. FIG. 1 is a diagram for explaining a network configurationaccording to the embodiment. As depicted in FIG. 1, a networkconfiguration 100 according to the embodiment includes an applicationserver 110, a tunneling apparatus 120 that functions as a distributionapparatus, and a communication terminal apparatus 130. The networkconfiguration 100 uses the UDLR and therefore, a unidirectionalcommunication network 140 a that is used when distribution data isdistributed from the tunneling apparatus 120 to the communicationterminal apparatus 130, and an IPv6 relaying network 140 b that isbidirectional communicable and used when transmission data istransmitted from the communication terminal apparatus 130 to thetunneling apparatus 120 are connected between the tunneling apparatus120 and the communication terminal apparatus 130.

In the network configuration 100, the application server 110 delivers tothe tunneling apparatus 120, application data that is to be distributedto the communication terminal apparatus 130. More specifically, theapplication server 110 outputs the application data to the tunnelingapparatus 120. Output to the tunneling apparatus 120 may be by aphysical line or a wireless means.

The “application data” is software data designed according to variouspurposes and is distributed to the communication terminal apparatus 130.More specifically, the application data is software that causes thecommunication terminal apparatus 130 to execute a specific function suchas given calculation, position searching, game playing, or playing ofcontents, or is data of contents to be played by the communicationterminal apparatus 130. The content of the application data is notparticularly limited.

The application data may be distributed to all the communicationterminal apparatuses 130 within a distribution area of the tunnelingapparatus 120. When the distribution data is distributed, the tunnelingapparatus 120 may distribute the distribution data only to a givencommunication terminal apparatus 130 by setting identificationinformation such as an address or distribution conditions. When thecommunication terminal apparatus 130 receives the application data, thecommunication terminal apparatus 130 may transmit arbitrary transmissiondata to the tunneling apparatus 120 that is the distribution sourceusing the IPv6 relaying network 140 b.

The tunneling apparatus 120 distributes to the communication terminalapparatuses 130 the application data delivered from the applicationserver 110 as distribution data. More specifically, the tunnelingapparatus 120 distributes (broadcasts) the distribution data to thecommunication terminal apparatuses 130 using the unidirectionalcommunication network 140 a. The tunneling apparatus 120 also acceptsthe transmission data transmitted as a response from the communicationterminal apparatus 130 that receives the distribution data.

The communication terminal apparatus 130 receives the distribution datafrom the tunneling apparatus 120. The communication terminal apparatus130 transmits arbitrary transmission data as a response to the tunnelingapparatus 120 using the IPv6 relaying network 140 b. More specifically,the communication terminal apparatus 130 includes an OS/application unit131, a receiving unit 132, and a communication processing unit 133.

The OS/application unit 131 functions as an interface for a user of thecommunication terminal apparatus 130. The OS/application unit 131accepts transmission data to be transmitted from the user to thetunneling apparatus 120. The receiving unit 132 is connected to theunidirectional communication network 140 a and receives distributiondata distributed from the tunneling apparatus 120.

The communication processing unit 133 transmits the transmission datareceived by the OS/application unit 131 to the IPv6 relaying network 140b that is a bidirectional communication network. When an error messagewith respect to the transmission data is transmitted as a response fromthe IPv6 relaying network 140 b, the communication processing unit 133detects the error message. When the communication processing unit 133detects the error message, the communication processing unit 133executes a given notifying process to notify the receiving unit 132 ofthe error message detected. The content of the notifying process of theerror message will be described in detail with reference to FIG. 2hereinafter.

(Error Message Notification Process)

A process by the communication terminal apparatus 130 executed when anerror message is transmitted from the IPv6 relaying network 140 b of thenetwork configuration 100 depicted in FIG. 1 will be described. In theembodiment, an example will be described where an error message “PacketToo Big” is transmitted to provide notification that transmission dataof a capacity exceeding the MTU representing the capacity transmittablein a network, has been transmitted.

FIG. 2-1 is a diagram for explaining the error message notificationprocess. FIG. 2-1 depicts the connection between the tunneling apparatus120 and the communication terminal apparatus 130. The unidirectionalcommunication network that distributes the application data(distribution data) from the tunneling apparatus 120 is depicted as anetwork 210 (corresponding to the unidirectional communication network140 a).

FIG. 2-2 is a list of addresses of configurations. As depicted in FIG.2-2, in a list 230, an address (for example, an IP address or an MACaddress) is set that designates each of the components as thetransmission source or a transmission destination of transmission data,for each of the components that functions as an interface when data istransmitted or received. In practice, addresses are also set for each ofthe relay apparatuses R1, R2, and R4 described hereinafter. However, theembodiment does not include any process to designate the addresses ofthe relay apparatuses R1, R2, and R4 and therefore, representation ofsuch addresses is omitted.

It is assumed that the transmission data transmitted from thecommunication terminal apparatus 130 is information having set therein arouter Z connected to the tunneling apparatus 120 as its transmissiondestination. As depicted in FIG. 2-1, the tunneling apparatus 120 andthe router Z are connected by I/F (interface) units 123 and 124.

The bidirectional communication network that transmits the transmissiondata from the communication terminal apparatus 130 to the tunnelingapparatus 120 is represented as a network 220 (corresponding to the IPv6relaying network 140 b). As an example, the relay apparatuses R1 and R2are disposed in the network 210 and the relay apparatuses R3 and R4 aredisposed in the network 220.

The receiving unit 132 of the communication terminal apparatus 130receives distribution data (SO) from the tunneling apparatus 120. Theuser of the communication terminal apparatus 130 transmits arbitrarytransmission data to a distributing unit 122 that is the distributionsource as a response to the distribution data. At this time, the datathat the OS/application unit 131 has accepted is transmitted as thetransmission data. The transmission data is output to the receiving unit132 that has received the distribution data from the OS/application unit131 (S1).

The communication terminal apparatus 130 realizes bidirectionalcommunication using the network that uses the UDLR. In practice, thereceiving unit 132 and the distributing unit 122 each executeunidirectional communication. However, viewing the processes of thereceiving unit 132 and the distributing unit 122 from the OS/applicationunit 131, the units 132 and 122 seem to function as an interface thatexecutes bidirectional communication. Therefore, the OS/application unit131 executes the same processes as those executed when theOS/application unit 131 is connected to an interface that executesbidirectional communication.

The receiving unit 132 executes a process to transmit the transmissiondata input from the OS/application unit 131, to the tunneling apparatus120. More specifically, to use the network 220 as a virtual network totransmit a response, the receiving unit 132 outputs the transmissiondata to the communication processing unit 133 (S2).

The configuration of the communication processing unit 133 will bedescribed. As depicted in FIG. 2-1, the communication processing unit133 includes a detecting unit 134, a setting unit 135, an errorprocessing unit 136, and an I/F (interface) unit 137. When thetransmission data is input from the receiving unit 132, thecommunication processing unit 133 transmits the transmission data fromthe I/F unit 137 to the network 220 (S3).

When the packet size of the transmission data transmitted from the I/Funit 137 is equal to or smaller than the MTU of the network 220, thetransmission data is sent to the tunneling apparatus 120 through therelay apparatuses R3 and R4. However, when the packet size of thetransmission data exceeds the MTU of the network 220, the relayapparatus R3 detects that the packet size of the transmission dataexceeds the MTU, and an error message “Packet Too Big” is transmitted tothe I/F unit 137 of the communication terminal apparatus 130 (S4).

When the error message “Packet Too Big” is transmitted from the relayapparatus R3, the communication processing unit 133 receives the errormessage through the I/F unit 137. The detecting unit 134, the settingunit 135, and the error processing unit 136 execute an errornotification process. The detecting unit 134 first detects the errormessage (S5). The setting unit 135 then sets data that is formed byincluding the error message in the transmission data, as newtransmission data (S6).

The error processing unit 136 finally executes a process of resolvingthe error detected by the relay apparatus R3, for the new transmissiondata set by the setting unit 135. In the embodiment, because the message“Packet Too Big” is detected, a process of adjusting the packet sizesuch that the transmission data has the capacity equal to or smallerthan the capacity of the MTU, is executed.

In this example, the process of resolving the error is a process ofvarying the packet size such that the capacity of the transmission databecomes equal to or smaller than the MTU, because the detecting unit 134has detected the message “Packet Too Big”. The error message “Packet TooBig” includes information that indicates the MTU of the network 220 andtherefore, the packet size may be adjusted referring only to thisinformation. The transmission data for which the process of resolvingthe error is executed by the error processing unit 136 is output againto the I/F unit 137 and is transmitted from the I/F unit 137 to thenetwork 220 (S7).

The transmission data having incorporated therein the error message istransmitted to the tunneling apparatus 120 through the relay apparatusesR3 and R4. The tunneling apparatus 120 receives the transmission datausing the receiving unit 121. The receiving unit 121 refers to theaddress attached to the transmission data received and outputs thetransmission data to the distributing unit 122 that is the transmissiondestination (S8).

When the transmission data having incorporated therein the error messageis input into the distributing unit 122 from the receiving unit 121, thedistributing unit 122 distributes this transmission data to thecommunication terminal apparatus 130 as distribution data (S9). When thedistribution at S9 is executed, the distributing unit 122 refers toidentification information (for example, an address) of the transmissiondestination of the transmission data and distributes the transmissiondata such that the distribution data reaches only the communicationterminal apparatus 130.

As described, usually, when the distributing unit 122 of the tunnelingapparatus 120 distributes the distribution data (for example, thedistribution at S0), numerous unspecified communication terminalapparatuses 130 are distribution destinations. However, in thedistribution at S9, distribution limited to the communication terminalapparatus 130 that is the transmission destination of the transmissiondata is executed to notify the apparatus 130 of the error message. Anyapproach may be used to execute the limited distribution.

When the receiving unit 132 of the communication terminal apparatus 130receives from the tunneling apparatus 120, the distribution data havingincorporated therein the error message, the receiving unit 132 extractsthe error message from the distribution data. The receiving unit 132adjusts the packet size of the transmission data according to the MTUincluded in the extracted error message “Packet Too Big”.

As described, the processes to give notification of the error areexecuted in the communication terminal apparatus 130 and the tunnelingapparatus 120. Therefore, error notification may be executed even usinga network configured by the UDLR such that an error message is reflectedon the network.

(Adjustment of Transmission Data in Error Message Notification Process)

To execute the error message notification process as depicted in FIG.2-1, a given adjustment must be executed with respect to thetransmission data. Hence, the details of the adjustment of thetransmission data in the error message notification process will bedescribed with reference to FIGS. 3 to 9.

FIG. 3 is a sequence chart of a transmission route of transmission data.As depicted in FIG. 3, transmission data 400 is input into the receivingunit 132 of the communication terminal apparatus 130. The transmissiondata 400 is the data accepted by the OS/application unit 131 depicted inFIG. 2-1.

FIG. 4 is a diagram of a configuration of the frame of the transmissiondata 400. It is assumed that the transmission data 400 is information tobe transmitted to the router Z. Therefore, as depicted in FIG. 4, thetransmission data 400 includes a user data packet 401, an IP packet 402,and an MAC packet 403.

The user data packet 401 is configured by data that is created by a userof the communication terminal apparatus 130. The data that is created bya user may be text data or may be video image data or music data, andthe type of data is irrelevant. The data is not limited to data createdby the communication terminal apparatus 130 and may be data prepared inadvance.

The IP packet 402 stores therein the IP address of the transmissionsource and the IP address of the transmission destination of thetransmission data 400. An IP address is an address set in advance ineach component that functions as an interface when data is transmittedor received. More specifically, the IP packet 402 is configured by theIP address (Src: IP-A) of the receiving unit 132 of the communicationterminal apparatus 130 that is the transmission source, and the IPaddress (Dst: IP-Z) of the router Z that is the transmissiondestination.

The MAC packet 403 stores therein the MAC address of the transmissionsource and the MAC address of the transmission destination of thetransmission data 400. More specifically, the MAC packet 403 isconfigured by the MAC address (Src: MAC-A) of the receiving unit 132 ofthe communication terminal apparatus 130 that is the transmissionsource, and the MAC address (Dst: MAC-Z) of the router Z that is thetransmission destination.

To simply the explanation, in the embodiment, it is assumed that therelay apparatuses R1 and R2 are not connected and the receiving unit 132of the communication terminal apparatus 130 and the I/F unit 124 of therouter Z are on the same segment. The address of the router Z itself isused as the MAC address that represents the transmission destination.The receiving unit 132 has set therein in advance the MTU that is thecriterion and the packet size is adjusted to be the maximum sizeaccording to the MTU.

In the example depicted in FIG. 2-1, an example where the processing isexecuted assuming that the initial value of the MTU of each of thenetworks 210 and 220 is 1,500 [bytes] will be described. As described,the MTU is a permissible magnitude of the data size that is set for eachnetwork and that is transmittable in one packet of transmission.Therefore, when the communication terminal apparatus 120 establishes aconnection to another network and thereby, executes the UDLR, adifferent MTU may be set (the MTU may also be MTU=1,500 [bytes]).Therefore, each time a connection is established, the packet size isadjusted to be the largest size that matches the MTU set.

The transmission data 400 is subject to encapsulation by the receivingunit 132 to use the UDLR and becomes transmission data 500. FIG. 5 is adiagram of the configuration of the frame of the transmission data 500.As depicted in FIG. 5, the transmission data 500 includes thetransmission data 400 to which an encapsulation header packet 501, anencapsulation IP packet 502, and an encapsulation MAC packet 503 areappended as packets concerning the encapsulation.

The encapsulation header packet 501 is a packet indicating that thetransmission data 400 is encapsulated. More specifically, for example,the encapsulation is executed using a GRE (Generic RoutingEncapsulation) protocol, etc.

The encapsulation IP packet 502 is configured by IP addresses of thecommunication processing unit 133 that is the transmission source andthe receiving unit 121 that is the transmission destination used whenthe encapsulation is executed. The encapsulation MAC packet 503 storestherein the MAC address (Src: MAC-B) of the communication processingunit 133 that is the transmission source and the MAC address (Dst:MAC-M) of a receiving interface of R3 that is the nearest transmissiondestination used when the encapsulation is executed.

The packet size of the appended packet portions 501 to 503 of thetransmission data 500 is an increased-portion size that is theincreased-portion size=α with respect to the transmission data 400. Asdescribed, the transmission data 400 is adjusted to have a packet sizethat is within the MTU (in this case, within 1,500 [bytes]). However,the transmission data 400 is appended with the increased-portion size=αand becomes the transmission data 500. As a result, the transmissiondata 500 has a packet size larger than the MTU. This increased-portionof the packet size generated by the encapsulation is one factor thatcauses the packet size to exceed the MTU. The value of theincreased-portion=α is stored in a memory, etc., such that the value maybe used in error processing described hereinafter.

The transmission data 500 is transmitted from the I/F unit 137 of thecommunication processing unit 133 to the network 220. The relayapparatus R3 detects that the transmission data 500 exceeds the MTU.Transmission data 600 including the error message “Packet Too Big” isreturned from the relay apparatus R3 to the I/F unit 137 of thecommunication processing unit 133.

FIG. 6 is a diagram of a configuration of the frame of the transmissiondata 600. As depicted in FIG. 6, the transmission data 600 is configuredby the transmission data 500 appended with an error message packet 601and a transmission destination IP address packet 602 to return thetransmission data 500 to the communication processing unit 133 of thecommunication terminal apparatus 130. The packet size of the entiretransmission data 600 is adjusted according to the MTU such that thetransmission data 600 may be transmitted by the relay apparatus R3 tothe network 220. More specifically, the adjustment is a process ofreducing the packet size to a size equal to or smaller than the MTU(1,500 [bytes]) by deleting a portion of the user data packet 401.

When the communication processing unit 133 receives the transmissiondata 600 that is returned from the relay apparatus R3 by the I/F unit137 (see FIG. 2-1), the detecting unit 134 (see FIG. 2-1) detects thatthe transmission data 600 is a packet encapsulated using the GREprotocol, etc. and is data that includes the error message packet 601.When the detecting unit 134 detects the transmission data 600 as datathat includes an error message, the detected data is set by the settingunit 135 as new transmission data.

The communication processing unit 133 extracts the MTU included in theerror message packet 601 and sets the extracted MTU to be the MTU of thenetwork 220. The communication processing unit 133 progresses to aprocess to transmit the new transmission data. The error processing unit136 extracts the increased-portion size=α added when the encapsulationis executed, from the transmission data 500. The error processing unit136 calculates a value by subtracting the increased-portion size=α fromthe value of the MTU extracted from the error message packet 601 as theMTU(α) to be referred to when the receiving unit 132 outputstransmission data. New transmission data 700 is created from thetransmission data 600 based on the MTU(α) calculated.

FIG. 7 is a diagram of a configuration of the frame of the transmissiondata 700. As depicted in FIG. 7, an error message packet 701 formed byrewriting the MTU (1,500 [bytes]) of the error message packet 601 of thetransmission data 600 to MTU MTU(α) is created and the packet size ofthe entire transmission data 700 is adjusted such that the MTU becomesMTU MTU(α). In this case, the packet size is also adjusted by properlydeleting the user data packet 401.

When the transmission data 700 is created, to distribute the errormessage packet 701 to the receiving unit 132 of the communicationterminal apparatus 130, the addresses of the transmission destinationsof an IP address packet 702 and an MAC address packet 703 are set to bethe addresses corresponding to the receiving unit 132 of thecommunication terminal apparatus 130 (IP address: IP-A, MAC address:MAC-A).

The addresses of the transmission sources of the IP address packet 702and the MAC address packet 703 of the transmission data 700 are set tobe the addresses of the relay apparatus R3 (IP address: IP-M, MACaddress: MAC-M) that has returned the transmission data 600 includingthe error message “Packet Too Big” to the I/F unit 137 of thecommunication processing unit 133 (see FIG. 6), or the addresses of therouter Z (IP address: IP-Z, MAC address: MAC-Z).

Encapsulation is again executed for the transmission data 700 created asdescribed above to transmit the data 700 from the network 220 to thetunneling apparatus 120. The transmission data encapsulated by the errorprocessing unit 136 has the configuration of transmission data 800described hereinafter. However, although the encapsulation executedagain may be executed by the error processing unit 136 as one method,this encapsulation may also be executed utilizing a processing method ofencapsulating an ordinary packet.

FIG. 8 is a diagram of a configuration of the frame of the transmissiondata 800. As depicted in FIG. 8, the transmission data 800 is configuredby the transmission data 500 added again with the packets (theencapsulation header packet 501, the encapsulation IP packet 502, andthe encapsulation MAC packet 503) concerning the encapsulation that areadded to the transmission data 500 depicted in FIG. 5. Theincreased-portion size of each of the packets is the increased-portionsize=α and the packet size of the entire transmission data 700 isMTU=MTU(α). Therefore, as a result, the packet size of the entiretransmission data 800 is a size that is within the MTU that is MTU=1,500[bytes].

The transmission data 800 processed by the error processing unit 136 istransmitted from the I/F unit 137 to the network 220. The transmissiondata 800 is received by the receiving unit 121 of the tunnelingapparatus 120. The receiving unit 121 decapsulates the encapsulation ofthe transmission data 800 received, and extracts transmission data 900.

FIG. 9 is a diagram of a configuration of the frame of the transmissiondata 900. As depicted in FIG. 9, the transmission data 900 is configuredby removing the packets (the encapsulation header packet 501, theencapsulation IP packet 502, and the encapsulation MAC packet 503)concerning the encapsulation, from the transmission data 800. That is,the transmission data 900 has the same configuration as that of thetransmission data 700.

The receiving unit 121 extracts the addresses (Dst: IP=A, MAC-A) of thetransmission destination that are set in the IP address packet 702 andthe MAC address packet 703, from the transmission data 900. Thereceiving unit 121 executes a process to distribute the transmissiondata 900 to the receiving unit 132 of the communication terminalapparatus 130 that the addresses represent. More specifically, thereceiving unit 121 outputs the transmission data 900 to the distributingunit 122. The distributing unit 122, using the network 210, distributesthe transmission data 900 to the receiving unit 132 of the communicationterminal apparatuses 130 having the destination addresses that are setin the packet.

The receiving unit 132 of the communication terminal apparatus 130uniquely receives distributed data (the transmission data 900)distributed from the network 210. As a result, the receiving unit 132receives the error message “Packet Too Big” transmitted from the relayapparatus R3, changes the value of the MTU for the network 210 to theMTU(α), and makes settings to transmit to the router Z, the transmissiondata of a packet size corresponding to the resulting MTU.

As described, according to the communication terminal apparatus, thedistribution apparatus, the error notification method, and the errornotification program, a relay apparatus may assuredly give notificationof an error via an error message regardless of the networkconfiguration. When the receiving unit 132 that is notified of an errortransmits again the transmission data to the distributing unit 122, thereceiving unit 132 changes the content of the transmission data suchthat the size of the transmission data becomes equal to or smaller thanthe MTU. More specifically, the receiving unit 132 executes anadjustment such that the size of each frame becomes equal to or smallerthan the MTU by deleting or dividing the capacity of the user datapacket 401 of the transmission data 400 depicted in FIG. 4.

When transmission data of a packet size larger than the MTU is desiredto be transmitted, the MTU of the error message received by thereceiving unit 132 of the communication terminal apparatus 130 may beset in the OS/application unit 131. In such an example, theOS/application unit 131 divides the transmission data into capacitiesthat each are the MTU, sequentially outputs the divided transmissiondata to be transmitted to the tunneling apparatus 120.

Taking into account the increased-portion of the packet to be added dueto the encapsulation, the MTU is the packet size that is reduced inadvance by the amount of the increased-portion. That is, exceeding theMTU due to the encapsulation may be prevented even using a response thatuses the UDLR. Therefore, the MTU is set to be the largest communicablepacket size and the transmission data may efficiently be transmitted.

The value of the MTU of a network varies for each connection as in theembodiment even when the same communication terminal apparatus transmitsdata. Therefore, even when the MTU is set once by the above errornotification process, the same process may be executed for eachconnection.

Further, the MTU set once using the error message may be stored and usedas the initial value of the packet size of transmission data for thenext session of transmission. When the MTU in the previous session oftransmission is used as the initial value as described, depending on thenetwork connected, the MTU may become smaller each time the errornotification process is repeated and as a result, the MTU may convergeto the smallest MTU. Therefore, a setting of using the previous MTU asthe initial value and a setting of using an MTU of a relatively largevalue as the initial value may be used in parallel.

The error notification method explained in the present embodiment may beimplemented by a computer, such as a personal computer and aworkstation, executing a program that is prepared in advance. Theprogram is recorded on a computer-readable recording medium such as ahard disk, a flexible disk, a CD-ROM, an MO, and a DVD, and is executedby being read out from the recording medium by a computer. The programmay be distributed through a network such as the Internet.

INDUSTRIAL APPLICABILITY

As described, the communication terminal apparatus, the distributionapparatus, the error notification method, and the error notificationprogram according to the present invention are useful for transmissionand reception of data using unidirectional communication such asbroadcasting and in particular, are suitable for error notificationbetween networks configured using the UDLR.

1. A communication terminal apparatus that receives using aunidirectional communication network and that transmits using abidirectional communication network, comprising: a receiving unit thatreceives distribution data distributed through the unidirectionalcommunication network; an accepting unit that accepts transmission datato be transmitted to a distribution source of the distribution datareceived by the receiving unit; and a communication processing unit thattransmits the transmission data accepted by the accepting unit to thebidirectional communication network, wherein the communicationprocessing unit comprises: a detecting unit that detects an errormessage concerning the transmission data from the bidirectionalcommunication network; a setting unit that sets the transmission datathat includes the error message detected by the detecting unit, to benew transmission data; an error processing unit that subjects the newtransmission data set by the setting unit to a process of resolving anerror corresponding to the error message; and a transmitting unit thattransmits the transmission data whose error has been resolved by theerror processing unit to the bidirectional communication network to usethe transmission data as the distribution data from the distributionsource.
 2. The communication terminal apparatus according to claim 1,wherein the error processing unit, when the detecting unit detects anerror message indicating that a capacity of the transmission dataexceeds than a permissible amount for the bidirectional communicationnetwork to which the transmission data is transmitted, executes aprocess of reducing the capacity of the transmission data into which theerror message is incorporated by an incorporating unit, to an amountthat is equal to or less than the permissible amount.
 3. Thecommunication terminal apparatus according to claim 1, wherein thereceiving unit extracts the error message from the distribution data,when the distribution data received by the receiving unit is thetransmission data that has been error-processed by the error processingunit.
 4. The communication terminal apparatus according to claim 3,wherein the accepting unit divides the accepted transmission data intothe permissible amount for the bidirectional communication network, whenthe error message extracted from the distribution data by the receivingunit indicates that the capacity of the transmission data exceeds thepermissible amount of the bidirectional communication network, and thetransmitting unit transmits the transmission data that has been dividedby the accepting unit.
 5. A distribution apparatus comprising: adistributing unit that distributes distribution data using aunidirectional communication network; and a receiving unit that receivestransmission data from a terminal that is a distribution destination ofthe distribution data, using a bidirectional communication network,wherein the distributing unit distributes the transmission data as thedistribution data to a terminal that is a transmission source oftransmission data that includes an error message received by thereceiving unit, when the receiving unit receives transmission data thatincludes an error message from a terminal.
 6. The distribution apparatusaccording to claim 5, wherein the distributing unit distributesidentification information of the terminal that is the transmissionsource of the transmission data including the error message received bythe receiving unit, by attaching the identification information to thedistribution data.
 7. An error notification method of a communicationterminal apparatus that receives by a unidirectional communicationnetwork and transmits by a bidirectional communication network, theerror notification method comprising: a receiving step of receiving,distribution data distributed through the unidirectional communicationnetwork; an accepting step of accepting transmission data to betransmitted to a distribution source of the distribution data receivedat the receiving step; a first transmitting step of transmitting thetransmission data accepted at the accepting step to the bidirectionalcommunication network; a setting step of setting, when an error messageis detected with respect to the transmission data from the bidirectionalcommunication network, the transmission data including the detectederror message to be new transmission data; an error processing step ofsubjecting the new transmission data set at the setting step to aprocess of resolving an error corresponding to the error message; and asecond transmitting step of transmitting the transmission data whoseerror has been resolved at the error processing step, to thebidirectional communication network to use the transmission data as thedistribution data from the distribution source.
 8. An error notificationmethod comprising: a receiving step of receiving via a bidirectionalcommunication network and by a transmitting unit of a distributionapparatus, transmission data from a terminal that is a distributiondestination of the distribution data; and a distributing step ofdistributing via a unidirectional communication network, by adistribution unit of the distribution apparatus and as distributiondata, the transmission data to the terminal that is a transmissionsource of the transmission data received at the receiving step andincludes an error message.
 9. An error notification program causing acomputer to execute the error notification method according to claim 7.10. A computer-readable recording medium storing therein an errornotification program that causes a computer to execute the errornotification method according to claim 8.